Aspirin is one of the most recognized medicines in the world. The benefits of aspirin for pain, inflammation, and heart health have caused some writers to suggest that it may be the most successful over-the-counter medicine in history. Aspirin has been marketed in many different delivery systems, including compressed tablets (e.g., Bayer® aspirin tablets), powders (BC® and Goody's® powders), and effervescent tablets (Alka-Seltzer® tablets).
Aspirin has been combined with different active ingredients, including caffeine (Anacin® tablets) and acetaminophen (Excedrin® tablets), and it has been combined with various buffers (Bufferin®, Ascriptin®, and Bayer® Plus tablets).
Aspirin has also been proposed for use in combination with various vitamins and minerals, such as in U.S. Pat. No. 4,491,574 (vitamin A) and U.S. Pat. No. 5,770,215 (multivitamins). One formulation that has proved to be commercially successful is the combination of aspirin and ascorbic acid (“vitamin C”) in an effervescent tablet (Aspirin® Plus C), which was introduced in Europe over thirty years ago. Current dosing for Aspirin® Plus C is one to two tablets, with each tablet containing 400 mg aspirin and 240 mg vitamin C.
Despite aspirin's long history of success, it suffers from some manufacturing drawbacks. Aspirin is very hygroscopic and degrades quickly in a humid environment.
One method that one skilled in the art might employ to reduce the vulnerability of aspirin to degradation is to form a tablet having two or more layers, with aspirin in one layer and acidic or basic ingredients in another layer. These tablets require special handling and are more expensive to make than single layer tablets, and it can be difficult to ensure that the separate active ingredients are present at the proper levels in the tablet.
Effervescent formulations typically contain, in addition to one or more active ingredients, an acid source and a carbonate or hydrogen carbonate salt as the principal components of an effervescent couple. Prior efforts in formulating effervescent tablets containing aspirin have required excess amounts of alkaline substances, such as sodium carbonate, sodium bicarbonate, or sodium citrate to provide a highly soluble composition in water. This results in increased levels of elemental sodium, which can be problematic for individuals who should reduce their sodium intake.
A single-layer, effervescent tablet has long been needed that can provide a high level of aspirin and rapidly dissolve in water, without requiring excess amounts of alkaline substances.